Conventionally, high quality, expensive Inertial Navigation Systems (INSs) are used to determine the geo-location and attitude of an earth-station antenna's base. Such geo-location and attitude information, coupled with angular position sensors (which describe the angular relationship between an antenna Line-of-Sight (LOS)) and detailed ephemeris information (which describes the location and inclination of the satellite of interest), can be used to compute pointing angles needed to point the earth-station antenna at the satellite of interest. Such an approach is considered an open-loop pointing approach.
Another option for determining the pointing angles for the antenna is to use a Received Signal Strength Indicator (RSSI) to report the strength of received radio frequency energy, which can be used to help find a satellite of interest. RSSIs measure a power level that a Radio Frequency (RF) device is receiving from a radio infrastructure at a given location and time. RSSIs often employ a broad-spectrum envelope power detector to sense the RF energy from a whole satellite transponder or from all the transponders on a particular satellite. Based on the received signal strength, the pointing angles for the antenna can be calculated.
Yet another option for determining the pointing angles is to use an envelope power detector to first find a certain, particularly strong satellite signal on a Direct Broadcast Satellite (DBS) service. Pointing then can be offset from the found signal to find the actual satellite of interest.
Another class of systems use beacon receivers to help solve the problem of properly pointing the earth-station antenna. This often introduces considerable cost and complexity to the system since beacon receivers operate on very low power satellite signals which, in turn, require that the beacon receiver have an exceptionally narrow bandwidth (on the order of a few hundred Hz for a small aperture antenna). This makes such systems extremely vulnerable to clock drift and Doppler frequency shift, and usually requires the use of Phase Lock Loop Low Noise Blocks (LNBs) along with a precision, temperature compensated ten MHz reference. The beacon to be tracked is usually found on one of the two possible polarizations, and is often located on the satellite transponder band edge. Further, not all satellites of interest are equipped or even provisioned to provide a suitable beacon signal. As a result, there is a strong likelihood that the system may not be able to use the satellite beacon (if present) due to a polarization mismatch, or, in the case of small instantaneous bandwidth or phased-array antennas, because the earth-station antenna is not able to see the beacon and the satellite transponder of interest at the same time.